This proposal is from Dr. Linda Sandell, a cartilage biologist in the Departments of Orthopaedic Surgery and Cell Biology and Dr. James Cheverud, a population geneticist and morphologist in the Department of Anatomy and Neurobiology. Using strains related to the super healing mouse (both recombinant inbred strains and an advanced intercross), we have defined phenotypes of articular cartilage regeneration and ear tissue regeneration and established a strong positive correlation between these two phenotypes. Furthermore, proof- of-concept studies demonstrate that the ability to heal articular cartilage may be associated with protection from post-traumatic osteoarthritis. This unique genetic resource will be used to test the association between ear wound healing, cartilage regeneration and osteoarthritis and to systematically identify genes that contribute to cartilage regeneration and thus to osteoarthritis development. The specific aims of the current grant proposal are: (1) Test the correlation between articular cartilage regeneration and osteoarthritis in recombinant inbred lines of LG/J and SM/J, mapping to approximately 10 cM (2) Determine the distribution of articular cartilage regeneration and osteoarthritis in the advanced intercross f LG/J and SM/J, mapping these regions to sub-cM intervals containing 1-5 genes (3) Determine the cell and molecular mechanisms responsible for established strain differences in cartilage and stem cell responses in the strains that represent extremes of healing, and (4) Using a systems-educated candidate gene approach, validate genes through our Lend an Ear for Osteoarthritis Campaign. The methods used to undertake these specific aims rely on the availability of recombinant inbred and advanced intercross strains of LG/J and SM/J with different abilities to regenerate cartilage and ear tissue combined with mouse surgical techniques for articular cartilage wounding and destabilization of the medial meniscus (DMM osteoarthritis model), analyzed by histology and micro-CT. Functional analyses of cartilage and stem cells will be performed in the strains that are extremes of healing. Proof of gene involvement will be established by using the DMM osteoarthritis model in knock-out mice. The outcome of this project will be the identification of genes affecting osteoarthritis development and articular cartilage regeneration in mice, providing high-quality candidates for probing the human genome.